Hi everyone, I have a homework question which I don't know how to answer. Here is the question:

Harry is walking in a marathon. He was intending to complete the marathons total distance of 42km in seven hours while keeping a steady pace of 6km per hour. He was going good for his first four hours but developed a cramp in his legs and stopped to rest for 18 minutes. By what percentage will he need to increase his walking speed for the rest of the marathon if he is still going to complete it in seven hours? Include steps to your answer.

Now, I'm not sure how to calculate this. I subtracted 18 from the last 3 hours of the marathon and got 2 hours and 42 minutes. I then converted this to a decimal (2.7) and then to a percentage (38.6 2s.f) but I'm not sure I'm on the right track. Another problem is that I'm supposed to incorporate algebra into my answer and I have no idea how to do so. Anybody willing to help me out and confirm whether I'm correct or not on my earlier calculation? Thanks all.

Jun 14th 2013, 07:08 AM

dokrbb

Re: Algebra and percentages - In need of helpful hints

Hi there,

So, we have the distance he covered during the first 4 hours, find the distance that has to be covered, which you can calculate in meters 42000 - (4*6000) = 42 000 - 24 000 = 18000m

The speed would be more confortable to be calculated as m/min, which gives you 6km/hr = 6000m/60min = 100m

He is left with 2hr42 min, or 162min - get now the speed with which he needs to cover those 18000m;

The percentage you can evaluate in the end, hope this helps,

Jun 14th 2013, 07:36 AM

Crystuls

Re: Algebra and percentages - In need of helpful hints

Hi there, thanks a lot for your reply! I think I'm beginning to understand a bit better now :)
So, I think I figured out the speed by using the calculator: 6.66667km per hour

Though I should round this to the nearest significant figure: 6.7km per hour. Please feel free to correct me if I am wrong, I need all the help I can get haha. Thanks again!

Jun 14th 2013, 07:57 AM

jpritch422

Re: Algebra and percentages - In need of helpful hints

looks good, crystuls!

Jun 14th 2013, 08:05 AM

dokrbb

Re: Algebra and percentages - In need of helpful hints

...and don't forget to express in percentage the increase you got

Jun 14th 2013, 08:17 AM

Crystuls

Re: Algebra and percentages - In need of helpful hints

I'm not sure i understand what the speed is (I'm pretty slow, sorry). What is the increase and how do I calculate this to a percentage?

edit: so was my percentage correct in my first post? The percentage is 38.6%?

Jun 14th 2013, 08:21 AM

dokrbb

Re: Algebra and percentages - In need of helpful hints

...but you already have the answer: the initial speed is 6km per hour, for the second part you have got ... 6.7km per hour, isn't it?